Studies for manufacturing semiconductor devices, optical devices and memory devices using unique electrical, optical and magnetic properties of nanomaterials are proceeding, and in order to make the devices using the nanomaterials, a technique, which can grow the nanomaterials at a desired position, is essential. For this, previously, these device structures were embodied by Top-down method by which a semiconductor thin film is grown first, and then structure is remained by etching at the desired position. However, if etching is conducted by this method, physical and chemical damages of the material deposited by the method are inevitable, and this fatal problem of this previous method serves as a barrier to embody active optical devices such as laser.
Due to the problems of the Top-down method, Bottom-up method, which selectively grows nanomaterials, is being studied and developed, and it has an advantage, which can grow a desired material at a desired position to a desired shape, not to introduce the etching process because its basic concept is different from the previous Top-down method. As this Bottom-up method, a method for forming microstructure through chemical reaction occurred in a solution is being actively studied because it is easy to low temperature and mass production. Among solution reactions, i.e., methods for growing crystals using chemical reaction occurred in a solution, a general method of hydrothermal synthesis is a method, wherein metals, inorganic oxides and inorganic hydroxides are mixed with a reaction solution and additives needed for crystal growth, the mixed suspension is put into a high pressure reactor, and then crystals are synthesized or grown at a temperature of about 300° C. or less and a self-pressure of about 100 Mpa. In the case of zinc oxide, it is known that crystals can be grown vertically after pretreating a substrate on a two-dimensional flat substrate or forming seeds of the crystal on the surface thereof.
This previous hydrothermal synthesis method has advantages that crystals can be grown at relatively lower temperature than a catalyst and vapor deposition method, and can be produced in bulk. However, because it soaks the substrate itself in the reaction solution of the high pressure reactor and reacts thereof, there is a limit that the temperature of the substrate and the solution should be same, and it is impossible to change the kind and the concentration of the solution as the reaction progresses. Further, there was a problem that it is impossible to inpour the reaction solution as the reaction progresses in order because all reactants should be mixed at the same time.